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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

High-speed video observations of natural cloud-to-ground lightning leaders - A statistical analysis

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Campos, Leandro Z. S. [1] ; Saba, Marcelo M. F. [1] ; Warner, Tom A. [2] ; Pinto, Jr., Osmar [1] ; Krider, E. Philip [3] ; Orville, Richard E. [4]
Número total de Autores: 6
Afiliação do(s) autor(es):
[1] Inst Natl Pesquisas Espaciais, BR-12227010 Sao Jose Dos Campos - Brazil
[2] South Dakota Sch Mines & Technol, Dept Atmospher Sci, Rapid City, SD 57701 - USA
[3] Univ Arizona, Inst Atmospher Phys, Tucson, AZ 85721 - USA
[4] Texas A&M Univ, Dept Atmospher Sci, College Stn, TX 77843 - USA
Número total de Afiliações: 4
Tipo de documento: Artigo Científico
Fonte: ATMOSPHERIC RESEARCH; v. 135, p. 285-305, JAN 2014.
Citações Web of Science: 36

The aim of this investigation is to analyze the phenomenology of positive and negative (stepped and dart) leaders observed in natural lightning from digital high-speed video recordings. For that intent we have used four different high-speed cameras operating at frame rates ranging from 1000 or 11,800 frames per second in addition to data from lightning locating systems (BrasilDat and NLDN). All the recordings were GPS time-stamped in order to avoid ambiguities in the analysis, allowing us to estimate the peak current of and the distance to each flash that was detected by one of the lightning locating systems. The data collection was done at different sites in south and southeastern of Brazil, southern Arizona and South Dakota, USA. A total of 62 negative stepped leaders, 76 negative dart leaders and 29 positive leaders were recorded and analyzed. From these data it was possible to calculate the two-dimensional speed of each observed leader, allowing us to obtain its statistical distribution and evaluate whether or not it is related to other characteristics of the associated flash. In the analyzed dataset, the speeds of positive leaders and negative dart leaders follow a lognormal distribution at the 0.05 level (according to the Shapiro-Wilk test). We have also analyzed how the two-dimensional leader speeds change as they approach ground through two different methodologies. The speed of positive leaders showed a clear tendency to increase while negative dart leaders tend to become slower as they approach ground. Negative stepped leaders, on the other hand, can either accelerate as they get closer to ground or present an irregular development (with no clear tendency) throughout their entire development. For all the three leader types no correlation has been found between the return stroke peak current and the average speed of the leader responsible for its initiation. We did find, however, that dart leaders preceded by longer interstroke intervals cannot present speeds of the order of 10(7) m s(-1). Finally, we have analyzed the impact of recoil activity during positive leaders over their average speed and the return stroke peak current. Even though the analysis considering the leader speed was not conclusive it was possible to show that there is no apparent minimum or maximum peak current value for return strokes preceded by leaders with or without recoil activity (considering the most common range of values in literature, 20-80 kA). (C) 2013 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 10/02716-5 - Caracterização das componentes-M e dos líderes de relâmpagos naturais a partir de observações de câmeras de alta resolução temporal e medidas de campo elétrico atmosférico
Beneficiário:Leandro Zanella de Souza Campos
Modalidade de apoio: Bolsas no Brasil - Mestrado
Processo FAPESP: 03/08655-4 - Programa Nacional de Monitoramento de Raios (PRONAR)
Beneficiário:Osmar Pinto Junior
Modalidade de apoio: Auxílio à Pesquisa - Temático